Semiconductor devices are fabricated on wafers usually made out of silicon. The wafers are then cut into individual substrates, tested, and then packaged. There are many different ways of packaging a substrate, including Ball Grid Arrays (BGA), Flip Chip, Multi-chip Modules, Chip-on-a-Board, etc. Many of these packaging techniques involve grasping the substrate with a vacuum pickup from one location, manipulating the substrate in some way, and then placing it back down onto another or the same location. For example, when using flip chip packaging, the substrate must be lifted from a tray containing the substrates, flipped, and then solder balls are mounted onto pads located on the substrates.
In order for the vacuum pickup to obtain a good temporary bond with the substrate, the substrate should be horizontal with respect to the vacuum pickup. In some cases, when the substrates are lying on a substrate tray, the substrates are not lying perfectly horizontal because they may not be fully seated within depressions built into the tray designed to hold the substrates. When the substrate is not fully horizontal with respect to the vacuum pickup the chances of the vacuum pickup being able pick up the substrate goes down. Should a substrate not be picked up, intervention is often required to fix the positioning of the substrate to permit the vacuum pickup to attach to the substrate.
Intervention is not desired in an efficient packaging process since it often requires stopping the packaging process and a human operator making the required adjustments. Intervention slows down the process and increases overall production costs.
Solutions using custom designed substrate trays can reduce the number of substrates that are not lying horizontally, but they typically require a special tray for each size and type of substrate. This increases the costs and overhead associated with the packaging process, especially in packaging plants that process a wide variety of different substrates.
Therefore, a need has arisen for a method and apparatus that can increase the probability of a vacuum pickup forming a solid bond with a substrate by ensuring that the substrates are lying horizontal with respect to the vacuum pickup.